Preparation, characterization and sintering of yttrium-doped ThO2 for oxygen sensors applications

Abstract

The preparation of Th1-xYxO2-x/2 ceramics, to be used as electrolyte in oxygen sensors for sodium-cooled nuclear reactors, was successfully undertaken from oxalate precursors. Such method was found to provide quantitative precipitation of the cations into Th1-xYx(C2O4)2.2H2O solid solutions up to x = 0.15 while a polyphase system was obtained for x = 0.22. The corresponding oxides were obtained through heat treatment in air at 500°C and characterized by the means of PXRD, SEM and statistical X-EDS measurements. The conditions for the densification of Th1-xYxO2-x/2 ceramics were further determined by dilatometry (T = 1575°C, t = 8 hours) resulting in densification rates up to 99%. Finally, a first estimation of the electric properties of the solids was undertaken by impedance spectroscopy. Electrical conductivity was found to increase linearly with the incorporation of Y 3+ content while the associated values of activation energy decreased, with a minimum value of 1.1 eV for Th0.85Y0.15O1.925.

Synthesis and Direct Sintering of Nanosized (MIV,MIII)O2‐x Hydrated Oxides as Electrolyte Ceramics

“…[35] The use of the so-called hydroxide route could then be considered as an easy and directp ath towards highly reactive and homogeneouso xide based powders with the general formula M…”

Emergence of defect fluorite structure in nano‐sized thoria through doping with some divalent transition‐metal ions

“…Among the oxides of quadrivalent metal ions possessing fluorite structure, thoria (ThO 2 ) is a very important inorganic material finding extensive use in many industrial applications, involving ceramics, catalysts, sensors, and as electrodes in nuclear industry . Its high melting point, high corrosion resistivity, lower thermal expansion and higher thermal conductivity permit it to be useful for applications under high‐temperature conditions .…”

“…Other than intense research on luminescent properties of thoria doped with rare‐earth cations, generation of oxygen vacancy defects through the addition of lower valent cations for the primary use as oxygen storage capacitor (OSC) in solid oxide fuel cells (SOFC) is of current interest . The recent work of Clavier's group deserves a mention where yttrium‐doped thoria compositions have been demonstrated for oxygen sensor applications . Understanding defect chemistry in ceria has reached an appropriate level due to the existence of a vast number of studies; achieving such a level in thoria requires the need for more investigations .…”

“…Among the oxides of quadrivalent metal ions possessing fluorite structure, thoria (ThO 2 ) is a very important inorganic material finding extensive use in many industrial applications, involving ceramics, catalysts, sensors, and as electrodes in nuclear industry. [1][2][3][4] Its high melting point, high corrosion resistivity, lower thermal expansion and higher thermal conductivity permit it to be useful for applications under high-temperature conditions. 5,6 Other than intense research on luminescent properties of thoria doped with rare-earth cations, [7][8][9][10][11][12][13][14][15][16] generation of oxygen vacancy defects through the addition of lower valent cations for the primary use as oxygen storage capacitor (OSC) in solid oxide fuel cells (SOFC) is of current interest.…”

“…[17][18][19][20][21][22][23] The recent work of Clavier's group deserves a mention where yttrium-doped thoria compositions have been demonstrated for oxygen sensor applications. 3 Understanding defect chemistry in ceria has reached an appropriate level due to the existence of a vast number of studies; achieving such a level in thoria requires the need for more investigations. 24,25 Realizing this, divalent transition-metal ion doping in thoria has been investigated following an epoxide mediated sol-gel synthesis.…”